Modern day engines must meet ever-more stringent emission regulations while remaining as fuel efficient as possible. Such engines may be designed to meet extremely strict NOx and particulate matter regulations. The use of high levels of exhaust gas recirculation (EGR) to reduce NOx emissions may have an unfortunate side effect of increasing the emission of particulate matter (PM) or soot. There may be multiple approaches to achieve the emission targets and to reduce the particulate matter to levels which current after-treatment systems may be able to tolerate, each approach having its own advantages and disadvantages. Besides strategies like high injection pressure and late injection timing, after-treatment systems may be used to reduce both the NOx and particulate matter, but at a relatively higher initial coast for the engine/after-treatment system. This higher cost and complexity may result in a potential benefit for an in-cylinder emission reduction solution.
To meet the goals of reduced emissions and fuel efficiency, combustion chamber design may provide an opportunity to improve burn rate and fuel consumption while improving the fuel-air mixing rate so that particulate emissions may be reduced. High injection pressure systems may provide not only small droplets and more oxygen entrainment in the fuel/air mixture, but also may provide high momentum jets of fuel, which may be used to distribute the fuel to oxygen-rich regions within the combustion chamber. Due to the increased lift-off length and oxygen entrainment from the high injection pressure, the burning zone may now be moved closer to the bowl wall.
Traditional combustion system development has concentrated on axial symmetric bowl shapes. The traditional piston bowl shape may serve as a starting point for improvement, however, these shapes are generally 2-dimensional (smooth surfaced).